1. Field of the Invention
This invention relates to bending glass sheets, and particularly relates to bending glass sheets by the gravity sag technique into shallow bends required for certain windshields. This invention more particularly concerns bending pairs of glass sheets simultaneously to a shape of gentle curvature for subsequent lamination to form curved, laminated windshields of a particular curved shape, but which may require the shaping of glass sheets of slightly different outline contour to said particular curved shape without requiring a change of molds for the shaping operation.
Laminated, curved glass windshields have been produced by gravity sag bending on outline bending molds of rigid metal rail construction that have had the metal rail construction reinforced either by cross bracing within the outline of the mold or by rigidly connecting the outline mold to an exterior bracing frame or a combination of the two reinforcement techniques. Glass sheets have also been bent on continuous outline molds that are adjustable in shape by connecting relatively flexible glass supporting members to a rigid reinforcing frame. In bending glass sheets to relatively deep bends by the gravity sag method, it has been customary to use outline molds comprising rigid shaping rails that include one or more shaping rails pivoted to other shaping rails rigidly connected to a mold supporting frame. Some molds of this type have shaping rails that are replaceable to provide different shapes without requiring replacement of the entire mold.
To the best of our knowledge, the prior art has not provided an outline bending mold of the gravity sag type having a permanent shaping surface that conforms to the shape desired for the glass sheets after bending and is likewise capable of micrometer adjustment in outline size only without changing the curvature provided by the upward facing outline shaping surface of the bending mold. Such a mold would be useful during the course of an automobile model year when the outline contour required of the glass windshield must be changed slightly in one or both dimensions without changing the shape of the bent glass so that a glass sheet of a particular shape but of a slightly different outline contour conforming to a change in styling may be shaped on the same complement of outline molds as the glass sheets conforming to the original contour. Frequently, the adjusted contour required for the glass is sufficiently smaller than the original contour so that the bent glass sheet cannot be supported on the bending mold as developed for the original pattern even though the shape required for the glass is unchanged. Also, in case the opening for the windshield is increased without changing the shape thereof, a larger glass sheet supported on a mold of unchanged size would tend to develop a reverse lip around its marginal portion that lies beyond the portion of shaped glass sheet that sags to conform to the shaping rail. Such a reverse lip makes it difficult to install the shaped windshield in a shaped frame to receive the windshield.
In addition, since laminated windshields for compact cars which consume less gasoline are smaller and comprise thinner glass sheets than has been the case previously, some losses have been experienced because of glass sheets sliding relative to the mold shaping surface when they are accelerated rapidly from a position of rest where they are loaded onto the mold to a relatively high speed at which they are conveyed through a tunnel-like bending lehr where the glass is exposed to sufficient heat to cause it to sag to conform to the outline shaping surface of the mold.
2. Description of the Prior Art
U.S. Pat. No. 1,999,558 to Black discloses an outline mold comprising a pair of shaped bars that support the longitudinal side edges of the bent glass interconnected rigidly to transverse end rods to form a continuous mold shaping surface that supports the bent glass sheet and edge engaging members that engage the longitudinal extremities of the glass and that pivot to follow the glass extremities as the glass sags into engagement with the curved bars. The force applied against the engaged longitudinal extremities of the glass mars the longitudinal extremities of the glass.
U.S. Pat. No. 2,297,315 to Owen discloses a flexible shaping mold of the outline gravity sag type that is adjustable both as to shape and outline and is connected through adjustment members to a peripheral frame of rigid construction. The shaping member is either a continuous flexible band such as a helically coiled spring or a continuous notched band having notches provided along its alternate edges to impart flexibility to the shape of the mold as distinguished from its contour. Such bands are capable of assuming various curvatures and outlines when adjusted. While this patent states that the mold is sufficiently strong to withstand the weight of glass and is flexible only under the application of a greater force, the fact that the molds comprise endless shaping rails makes it difficult to avoid stressing the mold into distortion to compensate for distortion in outline at locations other than the locations where localized stress is applied to alter the mold outline contour.
U.S. Pat. No. 2,720,729 to Rugg; U.S. Pat. No. 2,798,338 to Jendrisak; U.S. Pat. No. 3,023,543 to Laine and Hagedorn; U.S. Pat. No. 3,265,489 to Garbin; U.S. Pat. No. 3,278,288 to Leflet; U.S. Pat. No. 3,408,173 to Leflet; and U.S. Pat. No. Re 27,634 to Cypher all disclose outline molds that have little or no interior bracing and are braced by rigid connections to a rigid outer member.
U.S. Pat. No. 3,484,226 to Golightly discloses an outline mold comprising notched shaping rails whose notches interfit with one another to provide different outlines for supporting glass sheets of different sizes to be bent. The differences in dimensions of shapes that can be supported on the Golightly molds are of finite variation depending upon the thickness of the rails and the width and spacing between notches.
U.S. Pat. No. 2,766,555 to Jendrisak and Carson discloses supporting outline ring molds in a tilted plane about an axis extending transverse to the path of mold movement through a bending lehr having a hotter temperature near the roof and a lower temperature near the floor of the lehr to help shape glass sheets to a non-uniform shape.
U.S. Pat. No. 3,233,996 to Cox, McKelvey and Reese discloses outline bending molds for shaping glass sheets to a complex curvature wherein during a bending operation, the molds are tilted about an axis extending transverse to the path of movement the glass sheet takes through a bending lehr having a vertical temperature gradient similar to that of the Jendrisak and Carson patent. Both of these latter patents show supporting glass sheets obliquely in order to enhance non-uniformity of bend.